Sunday, October 26, 2008

reaching out to the interwebs for math help

OK kids, this post is in no way interesting. I'm asking for some Algebra help. If you can't help me in Algebra, you can just stop reading now-- I promise this post will put you to sleep.

OK, so I'm studying for the GRE. Two of my first few practice tests were Basic and Advanced Algebra. I haven't taken Algebra since 1990. In college I tested right out of it and moved on to Calculus (which was clearly a genius plan since at the ripe old age of 32 I can barely remember how to multiply 2 parenthetical sets without looking it up. But hey, that's why I'm studying).

So, in my first 40 questions, I came across 4 that I just stared at with big blank eyes and wondered if really, this was a real question, honestly, I have absolutely no idea how to come up with this sort of information. They all seem to be the same question, but since I don't know what I'm looking for, the internet has been of little help in the research category. SO, I thought I'd reach out to my readers. Surely one of you can point out what's I've no doubt right in front of my face and make me feel foolish for not knowing it.

2. If Sally can paint a house in 4 hours, and John can paint the same house in 6 hour, how long will it take for both of them to paint the house together?

3. Jim can fill a pool carrying buckets of water in 30 minutes. Sue can do the same job in 45 minutes. Tony can do the same job in 1 ½ hours. How quickly can all three fill the pool together?

A. 12 minutesB. 15 minutesC. 21 minutesD. 23 minutesE. 28 minutes

9. If Steven can mix 20 drinks in 5 minutes, Sue can mix 20 drinks in 10 minutes, and Jack can mix 20 drinks in 15 minutes, how much time will it take all 3 of them working together to mix the 20 drinks?

10. If Sam can do a job in 4 days that Lisa can do in 6 days and Tom can do in 2 days, how long would the job take if Sam, Lisa, and Tom worked together to complete it?

A. 0.8 daysB. 1.09 daysC. 1.23 daysD. 1.65 daysE. 1.97 days

Clearly it is important to the people that let me into grad school that I know how to solve these sorts of issues, but honestly? Those 4 questions above might as well be written in Farsi, that's how absolutely empty I am on ideas how to solve them.

5 Comments:

holy cow, I have no idea...and I took the GRE only four years ago! I don't remember any questions like this on my review or on the test (and I scored much higher on the math part of the test). I bought one of the Princeton Review books or something similar to that at B&N and studied from that--if I recall correctly, the book goes into explaining how to get all the answers. Maybe you could "study" at B&N one day and look up the answer!

Superman has you on the right track, and you can apply the reasoning behind his formula to solve the rest.For any of these, I think the best way to approach the issue is by trying to figure out how much of something can get done per 1 unit of time increment.

So for the first problem you get:

1/4 + 1/6 = Amount of house the two can get done in 1 hour

Find the common denominator (12), and you find they get 5/12 of a house done in 1 hour.

Since your goal is to find the number of hours for 1 house, you can divide 1 by the house per hour, or 5/12. In math terms, that means flipping the numerator and denominator, so you get 12/5 = 2.4 = 2hrs, 24 min.

Now take a similar approach for the second problem. First, find out how much of the pool they can all fill in 1 minute. That would be:

1/30 + 1/45 + 1/90 = Amt in 1 min. = 6/90 pools in 1 min.

Since the goal is to find the time to fill 1 pool, again divide 1 by your result of 6/90, which by flipping the fraction gets you 90/6 = 15 minutes.

Question 3 throws you a little trick, since they are asking for the time to make 20 drinks (20 units, instead of 1 unit like the first two questions). But you tackle it just the same, by establishing how many drinks per minute the combined group can make. So in this case:

Now, since they asking for the amount of time for 20 drinks, divide 20 by your result of 220/30, which for math purposes means flipping the fraction and then multiplying by 20. That equals 600/220, or 2 min, 44 sec.

Now apply the same method to the last problem, and see if get the answer.